The present invention relates to automatic tuning devices for stringed instruments, i.e., fretted instruments such as guitars, and banjos or bowed instruments such as violins, cellos, or double basses. Instruments of these types rely for the pitch of their musical notes on the tension of the several musical strings that run from the body along a fingerboard to a head where the strings are attached to respective tuning pegs. It is the nature of the strings to stretch somewhat over time, especially while the instrument is being played. Stretching of the strings causes the tension to reduce, so that the instrument goes flat after a short time.
A number of proposals for automatic tuning devices appear in the literature, but these have not been widely accepted. Clark U.S. Pat. No. 2,624,027 employs a motor control system to tension a vibrating filament. Scholz U.S. Pats. Nos. 4,375,180 and 4,426,907 describe an automatic self-tuning device for guitars, using electrical contacts that make or break to energize an electric motor that controls the string tension. Skinn et al. U.S. Pat. No. 4,803,908 describes a digital tuning system in which each string of a guitar has an associated tuning arm and stepper motor. A transducer senses the pitch of the vibrating strings and adjusts the string tensions accordingly. Murata et al. U.S. Pat. No. 4,928,563 relates to an electronic tuning apparatus for electric guitars in which pitch information is extracted from the instrument during playing, and a small motor is energized for each string to adjust the string tension.
An unfortunate characteristic of stringed instruments is that the strings have to re-tuned continually in order for them to maintain their pitches. How often retuning is necessary varies widely from one instrument to the next, but as a rule guitar players have to retune after playing a maximum of about six or seven selections. This is quite inconvenient, especially for performing musicians. This is even more of a problem for rock guitarists who, by the nature of their music, require more retuning of their instruments than normal. In fact, it is common practice for a rock guitarist to have several "in-tune" instruments on hand for a concert, and to quickly change the instrument when the instrument in use goes out of tune. This practice requires an assistant to constantly retune the spare instruments on stage during a concert.
Quite clearly, it has long been desired for guitarists and other instrumentalists to play instruments that maintain their pitch over a long period of time, and preferably over the entire lifetime of the string. On the other hand, any automatic tuning device should not affect the purity, richness, tone, and crispness of the sound of the instrument, which can degrade if an active electromechanical device is connected to the strings.